Solid line = floor (spellings that unambiguously belong to the group). Shaded band up to the dashed edge = ceiling (the most it could reach if every ambiguous spelling counted here).
Diana was more common in the past and has since settled at a lower, steady level. All-time it's been given to 426,127 U.S. babies, the 532nd most common name by sound today, peaking at 11,230 in 1957, with 1,345 in 2025.
By sound, Diana also includes the spellings Dianna.